1. Field of the Invention
This invention relates to the preparation of stable aqueous polymer dispersions which contain an alkenyl-aromatic polymer compound.
2. Discussion of the Background
In order to obtain, for example, stable aqueous dispersions based on styrene and acrylic esters or butadiene, the monomers on which the copolymers are based are polymerized, as is well known, in aqueous emulsion using polymerization initiators and emulsifiers, with or without polymerization regulators. About 2-5% by weight, based on the monomers, of an emulsifier, is required to ensure that the polymer particles formed during the polymerization remain dispersed in the aqueous medium. The relatively high emulsifier content of the aqueous polymer dispersion reduces the surface tension of the latter and is responsible for the more or less pronounced foaming of the dispersion during its use. If such dispersions are used as binders in paper-coating compositions, the emulsifier content reduces the binding power of the binder and lowers the wet strength of the paper coated with such a composition.
It is moreover known that polymer dispersions may be prepared in the absence of emulsifiers or in the presence of only small amounts of these. However, this results in a higher amount of coagulate than when preparing dispersions with high emulsifier content.